The invention relates to a process to produce an aqueous composition comprising shearing a mixture to produce a mini-emulsion and polymerizing the mini-emulsion to produce the aqueous composition wherein the mixture comprises at least one tackifier, at least one ethylenically unsaturated monomer, at least one surfactant, and water. The inventive aqueous compositions are useful as adhesives, including pressure sensitive adhesives, such as, for example, tapes, labels, stickers, decals, decorative vinyls, laminates, and wall coverings.
The production of water-based adhesives is conventionally accomplished in three basic steps. First, a latex of a vinyl polymer is prepared using emulsion polymerization processes well known in the art. In a separate step, a tackifier dispersion is prepared by combining at least one tackifier, at least one surfactant, and water and subjecting this mixture to high shear to produce a tackifier dispersion. Then, the tackifier dispersion is combined with the latex to produce an aqueous composition useful for preparation of a water-based adhesive.
Another process, which has been described in the art, involves the dissolution of a tackifier with at least one monomer in the preparation of the latex. This process avoids the tackifier dispersion step described in the previous process. However, this process is ineffective in that high scrap levels in the emulsion polymerization process can result. High scrap levels are undesirable since the yield of useful product is diminished and filtration problems can result. Therefore, there is a need for an improved process that combines tackifiers and latexes to produce an adhesive without undesirable scrap levels.
In accordance with this invention, a process to produce an aqueous composition is provided. The process comprises shearing a mixture to produce a mini-emulsion and polymerizing the mini-emulsion in the presence of an initiator to produce the aqueous composition; wherein the mixture comprises at least one tackifier, at least one ethylenically unsaturated monomer, at least one surfactant, and water.
This inventive process produces an aqueous composition that has the advantage of combining tackifiers and vinyl polymers prior to polymerizing. Therefore, the additional process step of dispersing a tackifier in the latex is not required. The invention is further advantageous in that the process uses mini-emulsion polymerization and avoids the process problems that occur when tackifiers and monomers are polymerized using conventional emulsion polymerization processes namely the production of undesirable scrap levels. The aqueous compositions are also advantaged over the art since the surfactant normally required to disperse the tackifier is not needed.
A process to produce an aqueous composition is provided. The process comprises shearing a mixture to produce a mini-emulsion and polymerizing the mini-emulsion in the presence of an initiator to produce an aqueous composition. The mixture comprises at least one tackifier, at least one ethylenically unsaturated monomer, at least one surfactant, and water.
Any tackifier known in the art that can yield the properties desired in the aqueous composition can be utilized. Generally, the tackifier can be selected from the group consisting of rosins, rosin derivatives, rosin esters, hydrocarbon resins, synthetic polyterpenes, natural terpenes, and the like. More particularly, useful tackifying resins include, but are not limited to, (1) natural and modified rosins and the hydrogenated derivatives thereof; (2) esters of natural and modified rosins and the hydrogenated derivatives thereof; (3) polyterpene resins and hydrogenated polyterpene resins; (4) aliphatic petroleum hydrocarbon resins and the hydrogenated derivatives thereof; (5) aromatic hydrocarbon resins and the hydrogenated derivatives thereof; and (6) alicyclic petroleum hydrocarbon resins and the hydrogenated derivatives thereof. Mixtures of two or more of the above-described tackifiers may be required for some formulations.
Natural and modified rosins and the hydrogenated derivatives thereof include, but are not limited to, gum rosin, wood rosin, tall-oil rosin, distilled rosin, hydrogenated rosin, dimerized rosin, and polymerized rosin.
Suitable examples of esters of natural and modified rosins and the hydrogenated derivatives thereof include, but are not limited to, the glycerol ester of rosin, the glycerol ester of hydrogenated rosin, the glycerol ester of polymerized rosin, the pentaerythritol ester of hydrogenated rosin.
Polyterpene resins generally result from the polymerization of terpene hydrocarbons, such as the bicyclic monoterpene known as pinene, in the presence of Friedel-Crafts catalysts at moderately low temperatures. Preferably, the polyterpene resins have a softening point, as determined by ASTM method E28-58T, of from about 80xc2x0 C. to about 150xc2x0 C.
Aliphatic petroleum hydrocarbon resins and hydrogenated derivatives thereof are generally produced from the polymerization of monomers consisting of primarily olefins and diolefins. Preferably, the aliphatic petroleum hydrocarbon resins have a Ball and Ring softening point of from about 70xc2x0 C. to about 135xc2x0 C.
Aromatic hydrocarbon resins include, for example, hydrocarbon resins derived from at least one alkyl aromatic monomer, such as, for example, styrene, alpha-methyl styrene and vinyl toluene, and the hydrogenated derivatives thereof The alkyl aromatic monomers can be obtained from petroleum distillate fractions or from non-petroleum feedstocks, such as, for example, feedstocks produced from phenol conversion processes.
An alicyclic petroleum hydrocarbon resin can be produced utilizing a hydrocarbon mixture comprising dicyclopentadiene as the monomer.
The ethylenically unsaturated monomer is at least one acrylic or vinyl monomer known in the art capable of substantially solubilizing the tackifier. The term xe2x80x9csubstantially solubilizingxe2x80x9d means that at least 75% by weight of the tackifier should form a single-phase liquid in the ethylenically unsaturated monomer at the concentration specified. The ethylenically unsaturated monomer can be added as a single type of monomer or as a mixture. Examples of suitable ethylenically unsaturated monomers, include, but are not limited to, styrenic monomers such as, for example, styrene, xcex1-methyl styrene, vinyl naphthalene, vinyl toluene, chloromethyl styrene and the like; ethylenically unsaturated compounds such as, for example, methyl acrylate, acrylic acid, methacrylic acid, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, ethylhexyl acrylate, ethythexyl methacrylate, octyl acrylate, octyl methacrylate, lauryl methacrylate, lauryl acrylate, glycidyl methacrylate, alkyl crotonates, vinyl acetate, di-n-butyl maleate, di-octylmaleate, acetoacetoxyethyl methacrylate, acetoacetoxyethyl acrylate, acetoacetoxypropyl methacrylate, acetoacetopropryl acrylate, diacetone acrylamide, acrylamide, methacrylamide, hydroxyethyl methacrylate, hydroxyethyl acrylate, acrylonitrile, and the like; and nitrogen-containing monomers, such as, for example, t-butylaminoethyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, N,N-dimethylaminopropyl methacrylamide, 2-t-butylaminoethyl methacrylate, N,N-dimethylaminoethyl acrylate, N-(2-methacryloyloxy-ethyl)ethylene urea, and methacrylamidoethylethyiene urea.
The surfactant can be any conventional surfactant or a combination of surfactants known in the art. Generally, the surfactant is at least one selected from the group consisting of an anionic surfactant and a non-ionic surfactant. Examples of preferred surfactants include, but are not limited to, alkali alkylsulfate, ammonium alkysulfate, alkylsulfonic acid, fatty acid, oxyethylated alkyphenol, sulfosuccinates and derivatives, and mixtures thereof. A list of suitable surfactants is available in the treatise: McCutcheon""s Emulsifiers and Detergents, North American Edition, MC Publishing Co., Glen Rock, N.J., 1997. Preferably, the surfactant provides droplet/particle stability, but results in minimal aqueous phase nucleation (micellar or homogeneous).
The surfactant can also be a polymerizable surfactant which are surfactants that contain a polymerizable double bond. Examples of polymerizable surfactants include, but are not limited to, Hitenol BC-10, Hitenol HS 20, and Hitenol HS 10 surfactants commercially available from Dai-ichi Kogyo Seiyaku Co. and TREM LF40 surfactant available from Cognis Corporation.
In general, the tackifier portion of the aqueous composition represents about 1 to about 40 wt. %, preferably about 2 to about 30 wt. % and most preferably, 4 to 20 wt. % of the total solids of the aqueous composition. The polymer from the ethylenically unsaturated monomer represents about 60 to about 99 wt. %, preferably about 70 to about 98 wt. %, most preferably from 80 to 96 wt % of the total solids of the aqueous composition. The surfactant represents about 0. 15% to about 8% of the total solids of the aqueous composition, preferably 0.5% to about 2%.
In another embodiment of this invention, the mixture further comprises a least one rubber compound. The rubber compound useful in the invention is capable of being combined with or substantially dissolved in at least one ethylenically unsaturated monomer. Natural and synthetic rubbers are useful in this invention. Natural rubbers are derived from natural sources as opposed to synthetic sources. Examples of suitable rubber compounds include, but are not limited to, natural rubber, butyl rubbers, isoprene rubbers, chloroprene rubbers including neoprene rubbers, polybutadiene rubbers, nitrile-butadiene rubbers, styrene-butadiene rubbers, polypentanamers, and ethylene-proplyene-diene terpolymers.
The tackifier, ethylenically unsaturated monomer, surfactant, and water can be combined in any order. However, all of these components must be present prior to shearing. In one embodiment of this invention, the tackifier is dissolved in at least one ethylenically unsaturated monomer to form a tackifier/monomer mixture, which is then dispersed in an aqueous medium comprising surfactant and water to form the mixture. The mixture then is sheared to form the mini-emulsion.
Shearing of the mixture produces a mini-emulsion. The shearing can be conducted by any means known in the art. Generally, shearing can be achieved using a high shearing device to form droplets ranging in size from about 50 to about 500 nanometers to form the mini-emulsion. Although not wanting to be bound by theory, it is believed that shearing the mixture to form small droplets, and thus forming the mini-emulsion, prior to polymerization, helps to ensure that the predominant nucleation site and subsequent polymerization site occurs within the droplets. This minimizes transport of the monomer from the droplets which can result in precipitation of the tackifier.
The mini-emulsion can be polymerized by any method known in the art to produce the aqueous composition. During mini-emulsion polymerization, the ethylenically unsaturated monomer are pre-emulsified as small uniform particles along with a purposely added hydrophobic component, in this case a tackifier, prior to free radical initiation. Suitable initiators include conventional initiators, such as, for example, ammonium persulfate, alkali persulfate, hydrogen peroxide, t-butyl hydroperoxide, di-benzoyl peroxide, lauryl peroxide, di-tertiarybutylperoxide, 2,2-azobisisobutyronitrile, benzoyl peroxide, and the like. Although not intending to be bound by theory, the tackifier retains the more water-soluble monomers within the original particles which are the locus of the polymerization. Hence, there is no second generation of particles as there is in conventional emulsion polymerization. The mini-emulsion, as described above, may also be polymerized as described in U.S. Pat. No. 5,686,518 and Wang et al., xe2x80x9cEmulsion and Miniemulsion Copolymerization of Acrylic Monomers in the Presence of Alkyd Resin,xe2x80x9dJournal of Applied Polymer Science, Vol. 60, pp. 2069-2076 (1996), each of which is incorporated in its entirety by reference.
The mini-emulsion polymerization process by which the aqueous composition is made may also require a reducing agent or a catalyst. Suitable reducing agents are those that increase the rate of polymerization and include, for example, sodium bisulfite, sodium hydrosulfite, sodium formaldehyde sulfoxylate, ascorbic acid, isoascorbic acid, and mixtures thereof.
Suitable catalysts are those compounds that promote decomposition of the polymerization initiator under the polymerization reaction conditions thereby increasing the rate of polymerization. Suitable catalysts include transition metal compounds. Examples of such catalysts include, but are not limited to, ferrous sulfate heptahydrate, ferrous chloride, chelated forms of ferrous sulfate heptahydrate and ferrous chloride, and mixtures thereof.
The glass transition temperature (Tg) of the ethylenically unsaturated monomer portion of the aqueous composition in accordance with the invention may be up to about 60xc2x0 C. For applications where film formation of the aqueous composition at ambient temperature is desirable, the Tg is preferably less than about 20xc2x0 C. For adhesives compositions, the glass transition temperature may preferably be in a range between xe2x88x9260xc2x0 C. and 10xc2x0 C. The Tg is determined using Differential Scanning Calorimetry (DSC).
The aqueous composition of this invention can be utilized to produce adhesives, especially pressure sensitive adhesives, coatings, and laminates. Pressure sensitive adhesives (PSA) are used in a variety of applications including tapes, labels, stickers, decals, decorative vinyls, laminates, and wall coverings.
An adhesive of the invention comprises the aqueous composition of the invention and may be prepared by techniques known in the art, e.g. as disclosed in U.S. Pat. Nos. 4,879,333 and 5,728,759, each of which is incorporated in its entirety by reference. For example, the aqueous composition of the invention may be coated onto a substrate using techniques known in the art (e.g. roll-coating, curtain coating, gravure printing, slot die coating) to produce an adhesive or coated composition. The substrate can be any common substrate, such as, for example, paper, polyolefin films such as polyethylene and polypropylene, metals such as aluminum and steel, glass, urethane elastomers and primed (painted) substrates, and polyesters, including, but not limited to, terephthalate-based polyesters such as polyethylene terephthalate. The adhesive or coating composition of the invention may be cured at room temperature (ambient cure), at elevated temperatures (thermal cure), or radiation cured.
The ethylenically unsaturated monomer portion of the aqueous composition retains the desirable properties of an acrylic PSA such as peel strength, loop tack, and shear strength while the tackifier portion of the aqueous composition compliments or enhances these properties. More specifically, the tackifier portion of the aqueous composition typically enhances the peel strength and loop tack. Adhesives of the invention also offer the advantage of being water-based and having significantly less solvent, less than 25 wt % to as low as 1 wt % and even zero volatile organic compound (VOC) content.
The aqueous composition of the invention may be used neat to provide a pressure sensitive adhesive (PSA). Alternatively, it may be combined with other PSA additives such as, for example, post-added tackifiers dispersions, plasticizers, solvents, defoamers, neutralents, preservatives, surfactants, and the like. Specific examples of such additives can be found in Raw Materials Index, published by the National Paint and Coatings Association, 1500 Rhode Island Avenue, N.W., Washington, D.C. 20005. Further examples of such additives and emulsion polymerization methodology may be found in U.S. Pat. No. 5,371,148, incorporated herein by reference in its entirety.
Post-added tackifier dispersions can be any tackifier dispersion known in the art. Examples of tackifier dispersions that can be post-added to the aqueous composition are disclosed in U.S. Pat. Nos. 4,526,577, 4,460,728 and 4,411,954,; all of which are herein incorporated by reference in their entirety. Particularly useful tackifier resin dispersions that can be post-added to the aqueous composition include, but are not limited to, dispersions of the tackifiers listed previously in this disclosure.
A preferred post-added tackifier resin dispersion in the invention comprises Tacolyn 1070, Tacolyn 3179 H, Tacolyn 4603; all of which are tradenames of tackifiers commercially available from Eastman Chemical Company.
Plasticizers useful in the invention are a known class of materials, sometimes called elastomer plasticizing oils. They include paraffinic hydrocarbons, aromatic hydrocarbons, esters of aliphatic and aromatic acids, and mixtures thereof. Plasticizers are disclosed in U.S. Pat. No. 2,551,600, herein incorporated by reference in its entirety.
A preferred plasticizer for use in forming the inventive adhesive is dioctyl phthalate, provided by Eastman Chemical Company. Any plasticizer known in the art can be utilized based on the adhesive properties desired. Examples of commercially available adhesive plasticizers include xe2x80x9cHercolyn DExe2x80x9d (Eastman Chemical Company), xe2x80x9cNeville NP 10xe2x80x9d (Neville Chemical Co.), and xe2x80x9cShellflex 371xe2x80x9d (Shell Chemical Co.).
Any solvent known in the art can be utilized based on the adhesive properties desired. Examples of solvents include, but are not limited to, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, isobutanol, ethylene glycol monobutyl ether, propylene glycol n-butyl ether, propylene glycol methyl ether, propylene glycol monopropyl ether, dipropylene glycol methyl ether, diethylene glycol monobutyl ether, trimethylpentanediol mono-isobutyrate, ethylene glycol mono-octyl ether, diacetone alcohol, TEXANOL(copyright) ester alcohol (Eastman Chemical Company), and the like. Such solvents and coalescing aids may also include reactive solvents and coalescing aids such as diallyl phthalate, SANTOLINK XI-100(copyright) polyglycidyl allyl ether from Monsanto, and others as described in U.S. Pat. Nos. 5,349,026 and 5,371,148, incorporated herein by reference.
Surfactants to be added to the aqueous composition can be any surfactant known in the art. Suitable surfactants utilized are as discussed previously in this disclosure. Other surfactants that are useful to add to the aqueous composition are acetylenic diols and ethyloxylated acetylenic diols. Examples of acetylenic diols include, but are not limited to, Surfynol 104PG, Surfynol 440, Surfynol PSA336; all which are produced by Air Products.
Neutralents to be added to the aqueous composition can be any neutralent known in the art. Suitable neutralents include, but are not limited to, alkali hydroxides and amines. Examples of alkali hydroxides include sodium hydroxide, potassium hydroxide, and lithium hydroxide. Examples of amines include ethanolamine, triethylamine, and dimethylethanolamine. Other suitable neutralents are ammonium hydroxide, zinc oxide, and ammonium complexes of zinc oxide.
Another additive that has been found useful to add to the aqueous composition is polyvinylpyrrolidone (PVP). PVP can be obtained as Luviskol K60 and Luviskol K90 commercially available from BASF.
This invention can be further illustrated by the following examples of preferred embodiments thereof, although it will be understood that these examples are included merely for purposes of illustration and are not intended to limit the scope of the invention unless otherwise specifically indicated.